This invention relates to a slide bearing assembly and, more particularly, to a slide bearing assembly that can be operated in slow- and high-pressure applications without oil refillings for a prolonged period.
To operate the drive mechanism of excavators such as construction machines, the respective parts of the mechanism are coupled together in a rotatable or swingable manner so that they can be driven with a cylinder and other actuators. Take, for example, a hydraulic shovel having a bucket coupled to the arm at the distal end. To perform excavation with the bucket, the bucket cylinder is reciprocated so that the bucket rotates or swings about the point where it is coupled to the arm. To this end, the bucket is coupled to the arm by means of a slide bearing assembly comprising a shaft and a bush.
FIG. 14 is a cross-sectional view of a prior art slide bearing assembly. As shown, a boss 1 has a bush 2 fitted therein. A dust seal 3 is pressed against both ends of the bush 2. A bracket 6 is provided at both ends of the boss 1 and a shim 5 is inserted in the gap between the boss 1 and each bracket 6. An O-ring 4 is fitted around each of the gaps. A shaft 7 is inserted through the bracket 6 at one end, the bush 2 and the bracket 6 at the other end. The shaft 7 is prevented from rotating by means of an engagement bolt 8 passing through the shaft 7 and the bracket 6 at one end. A grease feed hole 30 is formed that runs from the other end of the shaft 7 to the middle of the bush 2. A stopper 32 is threaded into one end of the feed hole 30, which is filled with grease 34.
During excavation, a slow but extremely large pressure is applied to the surfaces of the slide bearing assembly. Under the circumstances, the sliding surfaces must be amply supplied with a thick lubricant such as grease in order to prevent the occurrence of sticking, galling, uneven wear and other troubles in early periods. To this end, frequent grease refillings are necessary but the refilling operation is not always easy to perform.
Another problem with grease refilling is that the old grease which has turned liquid must be discharged out of the bearing before it is refilled with new grease. Such discharge and refilling operations are usually performed at excavation sites. The discharged liquid grease is disposed of by being scattered over the surface of the soil at the site but this can cause a pollution problem. With the recent concern over environmental protection, it is particularly desired to refrain from discarding or scattering the liquid grease over the soil surface during the preparation of housing sites and gardening operations in urban areas.
With a view to maintaining lubricity on the sliding surfaces for a prolonged period without refilling grease and other lubricants, various methods have been developed, as exemplified by embedding a solid lubricant in the sliding surface of a bush (see FIG. 15, in which the bush 2 has graphite particles 36 embedded in the sliding surface). Other methods include forming the bush of self-lubricating plastics or using unconventional means such as a magnetic bearing and a pneumatic bearing. However, magnetic and pneumatic bearings are not suitable for use in high-load applications. Bearings that use solid lubricants (e.g. graphite) or self-lubricating materials (e.g. plastics) also have their own limitations. In the former case, the touch between base metal parts makes the occurrence of microscopic "galling" unavoidable. In the latter case, the insufficient strength and hardness of self-lubricating materials may occasionally result in a sudden occurrence of abnormal wear or deformation (creep).